1. Field of the Invention
The present invention relates to a method and equipment for simulation which correct flare (local flare) locally occurring in the photo process of semiconductor manufacturing.
2. Description of the Related Art
Pattern formation technology in manufacturing a semiconductor device adopts optical lithography. The optical lithography refers to a method in which a desired pattern formed in a reticle as a photo mask is transferred to a sample substrate through a reduction optical system. Photosensitive resin called a resist is formed on the sample substrate. With the use of difference in the melting speed between exposed areas and unexposed areas by developing solution, a latent image of the transferred pattern is etched to desirably process material.
Exposure technology adopts optical proximity correction (OPC), in which the effect of traces in proximity to each other is calculated and corrected to transfer the fine pattern with high precision, in addition to optimizing the wavelength of exposure light and the structure of the reticle. A transferred image of the pattern is simulated in consideration of the illumination condition (NA and Sigma) and the exposure condition (the material of the resist and exposure wavelength) and the like of an exposure device, and the effect of optical proximity and correction values are calculated or determined by experiment, to correct the dimensions of the reticle.
Generally, when the optical proximity correction is carried out, an optical image of the layout of the photo mask (mask layout) is calculated by a simulator, and then the mask layout is so modified that the calculated optical image takes a predetermined shape. It is necessary as a precondition that the optical image outputted from the simulator precisely corresponds with actual one. The unevenness in the material of a lens of the exposure device and the specific characteristics thereof, however, cause scattering in the lens, so that the effect of scattering also has to be considered in the simulation. The effect of scattering, called local flare, is caused by the specialty of lens material which depends on the wavelength of exposure light (short wavelength represented by 193 nm) and the like. The effect of scattering becomes a main cause of unexpected deformation in the shape of a transferred pattern and in the width of traces. In an image surface, it is possible to approximate the local flare at even light intensity in a background which depends on the intensity transmittance of the photo mask.
Patent document 1: Japanese Patent Application Laid-Open No. 2001-272766.
In a conventional simulation method, when the dimensions of traces are enough larger than an exposure wavelength, it is possible to estimate the amount of local flare with sufficient accuracy. When there are traces the dimensions of which are equal to or smaller than the exposure wavelength, however, there is a problem that the amount of local flare cannot be obtained with high accuracy. As the pattern of a semiconductor device becomes finer and finer in recent years, it is desirable to develop a simulation method which estimates the amount of local flare with high accuracy even if a trace is fine.